Java 微服务之 SpringCloud快速入门day02 （二）Feign

1、简介

为什么叫伪装?

Feign可以把Rest的请求进行隐藏，伪装成类似SpringMVC的Controller一样。

你不用再自己拼接url，拼接参数等等操作，—切都交给Feign去做。

项目主页:https://github.com/OpenFeign/feign

2、实现

（1）引入依赖

org.springframework.cloud

spring-cloud-starter-openfeign

2.0.1.RELEASE

（2）添加注解

@EnableFeignClients

（3）创建UserClient接口:Feign客户端

根据服务名拿到了对应的ip地址和端口

package com.itzheng.consumer.client;

import com.itzheng.consumer.pojo.User;

import org.springframework.cloud.openfeign.FeignClient;

import org.springframework.web.bind.annotation.GetMapping;

import org.springframework.web.bind.annotation.PathVariable;

@FeignClient(“user-service”)

public interface UserClient {

@GetMapping(“user/{id}”)

User queryBuId(@PathVariable(“id”) Long id);

}

表示去user-service这个服务提供方去获取对应的值以及设置对应的参数（即封装远程调用）

（4）完善ConsumerController

package com.itzheng.consumer.web;

import com.itzheng.consumer.client.UserClient;

import com.itzheng.consumer.pojo.User;

import com.netflix.hystrix.contrib.javanica.annotation.DefaultProperties;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixProperty;

import lombok.val;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.cloud.client.ServiceInstance;

import org.springframework.cloud.client.discovery.DiscoveryClient;

import org.springframework.cloud.netflix.ribbon.RibbonLoadBalancerClient;

import org.springframework.web.bind.annotation.GetMapping;

import org.springframework.web.bind.annotation.PathVariable;

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RestController;

import org.springframework.web.client.RestTemplate;

import java.util.List;

import java.util.Map;

@RestController

@RequestMapping(“consumer”)

@DefaultProperties(defaultFallback = “defaultFallback”)

public class ConsumerController {

//@Autowired

// private RestTemplate restTemplate;

/*

@Autowired

private DiscoveryClient discoveryClient;

*/

@Autowired

private UserClient userClient;

@GetMapping(“/{id}”)

public User queryById(@PathVariable(“id”) Long id) {

return userClient.queryBuId(id);

}

@GetMapping(“/{id}”)

//@HystrixCommand(fallbackMethod = “queryByIdFallback”) //开启线程隔离和服务降级（HystrixCommand失败服务的指令）

/* @HystrixCommand(commandProperties = {

@HystrixProperty(name = “execution.isolation.thread.timeoutInMilliseconds”,value = “3000”)

})

*/

//fallbackMethod失败的时候调用的方法,成功 时候默认调用下面的方法

@HystrixCommand(

commandProperties = {

//设置请求的次数为10次当请求请求失败超过5次的时候打开熔断

@HystrixProperty(name = “circuitBreaker.requestVolumeThreshold”,value = “10”),

//短路多久以后开始尝试是否恢复，默认5s 这里设置为10s

@HystrixProperty(name = “circuitBreaker.sleepWindowInMilliseconds”,value = “10000”),

//出错百分比阈值，当达到此阈值后，开始短路。默认60%

@HystrixProperty(name = “circuitBreaker.errorThresholdPercentage”,value = “60”)

}

)

/*

public String queryById(@PathVariable(“id”) Long id) {

if(id % 2 == 0){

throw new RuntimeException(“”);

}

String url = “http://user-service/user/” + id;

String user = restTemplate.getForObject(url, String.class);

return user;

}

*/

//fallbackMethod失败的时候调用的方法,与成功时候调用的方法的名称可以不一样，但是返回值和参数必须相同

public String queryByIdFallback(Long id) {

return “不好意思，服务器态拥挤了”;

}

public String defaultFallback() {

return “不好意思，服务器态拥挤了”;

}

/*

@GetMapping(“/{id}”)

public User queryById(@PathVariable(“id”) Long id) {

//根据服务id获取实例

//List instances = discoveryClient.getInstances(“user-service”);

//从实例当中取出IP和端口

//ServiceInstance instance = instances.get(0);

//随机，论询、hash

//ServiceInstance instance = client.choose(“user-service”);

//String url = “http://”+ instance.getHost()+“:”+instance.getPort()+“/user/”+id;

//System.out.println(url);

//底层还是上述的代码，内部通过拦截器将请求拦截下来，

//获取到user-service自动去负载均衡后获取ip地址将user-service替换

String url = “http://user-service/user/” + id;

User user = restTemplate.getForObject(url, User.class);

return user;

}

*/

}

（5）完善ConsumerApplication：开启Feign功能

package com.itzheng;

import org.springframework.boot.SpringApplication;

import org.springframework.boot.autoconfigure.SpringBootApplication;

import org.springframework.cloud.client.SpringCloudApplication;

import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;

import org.springframework.cloud.client.discovery.EnableDiscoveryClient;

import org.springframework.cloud.client.loadbalancer.LoadBalanced;

import org.springframework.cloud.openfeign.EnableFeignClients;

import org.springframework.context.annotation.Bean;

import org.springframework.web.client.RestTemplate;

//@EnableCircuitBreaker

//@EnableDiscoveryClient

//@SpringBootApplication

@EnableFeignClients

@SpringCloudApplication

public class ConsumerApplication {

/* @Bean

@LoadBalanced

public RestTemplate restTemplate(){

return new RestTemplate();

}*/

public static void main(String[] args) {

SpringApplication.run(ConsumerApplication.class,args);

}

}

（6）删除这两个依赖，因为在Feign当中已经有了该依赖

全部依赖

<?xml version="1.0" encoding="UTF-8"?>

<project xmlns=“http://maven.apache.org/POM/4.0.0”

xmlns:xsi=“http://www.w3.org/2001/XMLSchema-instance”

xsi:schemaLocation=“http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd”>

cloud-demo

com.itzheng.demo

1.0.0-SNAPSHOT

4.0.0

consumer-demo

org.springframework.boot

spring-boot-starter-web

org.springframework.cloud

spring-cloud-starter-netflix-eureka-client

2.0.1.RELEASE

org.springframework.cloud

spring-cloud-starter-openfeign

2.0.1.RELEASE

（7）开启Feign熔断机制

去掉之前的注解

设置Feign当中熔断的超时时长，开启熔断功能

ribbom:

ConnectionTimeOut: 500 #如果500毫秒没有获取的请求异常就抛出异常

ReadTimeOut: 2000 #如果超过2000秒没有获取到请求返回的值就抛出异常

feign:

hystrix:

enabled: true #开启熔断功能

完善UserClient

创建UserClientImpl实现类

package com.itzheng.consumer.client;

import com.itzheng.consumer.pojo.User;

import org.springframework.stereotype.Component;

@Component

public class UserClientImpl implements UserClient {

@Override

public User queryBuId(Long id) {

return null;

}

}

完善UserClient类

package com.itzheng.consumer.client;

import com.itzheng.consumer.pojo.User;

import org.springframework.cloud.openfeign.FeignClient;

import org.springframework.web.bind.annotation.GetMapping;

import org.springframework.web.bind.annotation.PathVariable;

@FeignClient(value = “user-service” ,fallback = UserClientImpl.class)

public interface UserClient {

@GetMapping(“user/{id}”)

User queryBuId(@PathVariable(“id”) Long id);

}